The present disclosure relates to the subject matter disclosed in international application PCT/EP01/03165 of Mar. 20, 2001, which is incorporated herein by reference in its entirety and for all purposes.
The invention relates to a diode laser device comprising at least one laser diode, a power supply for the laser diode, a cooling device including a heat sink with the laser diode disposed thereon, and a coolant supply allowing a coolant to flow through the heat sink.
Such diode laser devices are known from the prior art. The problem with these is that it is only possible to check whether they are operating properly by measuring the emitted laser radiation with calorimetric measuring instruments or devices for measuring the optical power, and, depending on the configuration, measurement of the optical power may prove problematic.
This requires arrangement of a corresponding measuring head in the radiation path of the laser radiation, with the result that the diode laser device cannot be used for its intended purpose, for example, for pumping a solid-state laser during the measuring.
The object underlying the invention is, therefore, to so improve a diode laser device of the generic kind that simple monitoring of the operation is possible without interfering with use of the diode laser device.
This object is accomplished with a diode laser device of the kind described at the outset, in accordance with the invention, in that an operation monitoring device is provided, and in that the operation monitoring device detects a quantity representing the electric current flowing through the laser diode and a quantity representing the temperature of the coolant exiting from the heat sink and determines from these an operational quantity representing operation of the diode laser device.
The advantage of the solution according to the invention is that the operational quantity can be determined without interrupting the radiation path of the laser radiation, and, consequently, also while the diode laser device is being used for its intended purpose, for example, for pumping a solid-state laser.
The solution according to the invention has the further great advantage that determination of the operational quantity can be carried out with simple means, as merely determination of the quantity representing the current flowing through the laser diode and the quantity representing the temperature of the coolant exiting from the heat sink is required, and these can be detected with simple means.
A multiplicity of direct and indirect methods are conceivable for detecting the quantity representing the temperature of the coolant exiting from the heat sink. If, for example, the coolant exiting from the heat sink is cooled to a certain temperature, it is conceivable to detect the cooling power required for the cooling.
For reasons of simplicity, however, it is particularly advantageous for the operation monitoring device to detect the temperature of the coolant exiting from the heat sink by means of a sensor.
For even more precise determination of the operational quantity, it has proven advantageous for the operation monitoring device to determine a quantity representing the temperature difference between the coolant entering the heat sink and the coolant exiting from the heat sink.
Such determination of the quantity representing the temperature difference can be carried out, for example, indirectly by determining the cooling power required for reaching a specified temperature for the coolant entering the heat sink.
It is, however, particularly simple for the operation monitoring device to detect the temperature of the coolant entering the heat sink by means of a sensor.
In principle, the operational quantity can be determined with sufficient precision on the basis of the temperature measurements, but the precision can be further increased by the operation monitoring device detecting the flow rate of the coolant through the heat sink.
This can be accomplished directly with particular advantage by the operation monitoring device detecting the flow rate of the coolant through the heat sink with a flowmeter.
A particularly favorable solution allowing the operational quantity to be determined with a high degree of precision provides for the operation monitoring device to determine a thermal quantity representing the thermal output conducted away from the laser diode by the cooling device and enabling the thermal output that is not emitted by the laser diode in the form of radiation to be determined at least approximately.
In principle, when determining the quantity representing the electric current flowing through the laser diode, it is conceivable to detect setting parameters of the power supply from which one can at least indirectly draw conclusions about the electric current flowing through the laser diode.
With a view to determining the operational quantity as precisely as possible, it is, however, particularly expedient, in particular, in order to determine the changes in the operational quantity as exactly as possible, for the operation monitoring device to comprise a current measuring device for determining the electric current flowing through the laser diode.
In the case of a laser diode it can be assumed that the voltage dropping at it will be approximately constant. However, in order to determine the operational quantity with as high a degree of accuracy as possible, provision is preferably made for the operation monitoring device to comprise a voltage measuring device for determining the voltage dropping at the laser diode during operation.
When determining the operational quantity, a particularly high precision is achievable by the operation monitoring device determining an electrical quantity representing the electric power supplied to the laser diode, which constitutes the total electric power supplied to the laser diode.
A particularly high accuracy is achievable in determining the operational quantity when the operation monitoring device determines the operational quantity from the electrical quantity and the thermal quantity.
In addition to the electrical quantity and the thermal quantity, other parameters may be incorporated into the determining of the operational quantity.
It is preferable for the parameters incorporated into the determining of the operational quantity to be selected such that the operational quantity represents the optical output power of the laser diode, so that the operational quantity is a direct measure of the optical output power of the laser diode and therefore directly supplies the most important information for operation of the laser diode.
Regarding the configuration of the diode laser device it has merely been assumed that this comprises one laser diode. However, the solution according to the invention can be utilized with particular advantage when the diode laser device comprises several laser diodes.
In this case, the several laser diodes are preferably fed by a common power supply.
The operational quantity can also be advantageously determined with sufficient precision when the quantity representing the electric current flowing through the entirety of the laser diodes is determined.
A quantity representing the electric current flowing through the totality of the laser diodes and a quantity representing the voltage dropping at the entirety of the laser diodes are therefore preferably incorporated into the electrical quantity, for which purpose the laser diodes are electrically connected in series.
When several laser diodes are provided in the diode laser device, the determining of the quantity representing the temperature of the coolant exiting from the heat sink also focuses on the temperature of the coolant exiting from the totality of the heat sinks.
Coolant preferably flows in parallel through the heat sinks of the several laser diodes so that each of the laser diodes is subjected to substantially the same cooling power.
Details of the design of the cooling device will now be given. It is, for example, conceivable to conduct the coolant exiting from the heat sink or heat sinks away freely. It is, however, particularly advantageous for the cooling device to comprise a cooling circuit from which the heat is conducted away via a heat exchanger.
Details of the way in which the operation monitoring device according to the invention operates will now be given. It is, for example, conceivable to operate the operation monitoring device continuously and to thus determine the operational quantity continuously.
It is, however, sufficient to determine the operational quantity after specified time intervals or after specified operating cycles, as it can usually be assumed that the operational quantity will change only slowly and not necessarily abruptly.
Further features and advantages of the solution according to the invention will be apparent from the following description and the appended drawings of an embodiment.